As is known, analog signals can be digitized by scanning their pattern with a specific frequency, so that pulses are obtained with an amplitude corresponding to the deflection of the information signal at the time of the particular scan. The numerical value of the amplitude of the scanning pulse is then converted into binary form and said binary signal is recorded on the particular record support. When reproducing a signal recorded in this way, the binary values of the amplitudes of the successively following scanning pulses are converted back into the corresponding analog pattern of the information signal.
The transition from level 0 or -1 to level +1 in the binary signal can be considered as the rising front of a single pulse in the binary signal. The transitions from level +1 to level 0 or -1 can be looked upon as the falling front of the single pulse. The binary signal, which reproduces the numerical value of the amplitude of one of the scanning pulses, normally contains several such single pulses and consequently also transitions between the -1 and +1 levels. The length located in the binary signal between two transitions is referred to hereinafter as the "run length" or just as "signal". A run length may comprise only a single bit or several directly succeeding bits or bit positions of the same level and/or value 0 or 1. Thus, the run length also gives the duration of the individual pulses in the binary signal.
If in a single binary signal, several single pulses succeed one another, wherein each comprises only one or only a few bit positions, then the time interval between the rising front and the falling front of the single pulse, i.e., the duration of the particular single pulse, is very short. The shorter the run length of the single pulse, the greater the demands on the width of the frequency spectrum to be transmitted by the system.
When recording the binary amplitudes of scanning pulses, problems occur if a binary-expressed numerical value of the amplitude of a scanning pulse has a frequent change of level between 0 and/or -1 and +1. In such a binary signal, the run lengths of the single pulses are short. In the case where such a signal is to be recorded, the pulse ratio is high and the demands made on the necessary frequency width of the system are correspondingly high. If the system does not have the necessary frequency width, then the single pulses are reproduced in distorted form in the binary form of the scan value.
In order to obviate this and other problems, the binary-expressed values of the amplitudes of the scanning pulses to be recorded are treated on the basis of a run-length code. A large number of such codes are known. One of the purposes for using such a code is that if the single pulses are short, the binary form is transformed in accordance with a given rule. In addition, if the single pulse happens to be large, the code can cause the time interval between its edges or sides to be reduced, in order to save space on the record support. One such run-length code called HDM-1 (cf J. Audio Eng. Soc., Vol. 31, No. 4, 1983, pp. 228-234) provides run lengths or edge spacings between 1.5 T and 4.5 T, which can be varied in 0.5 T steps. T is the time or correspondingly the length necessary for recording s single bit cell of said code.
Certain problems occur when reproducing a binary signal recorded in this way. For example, the edges of a response or a single pulse in the reproduced binary signal has a finite instead of an infinite steepness. The 0 crossings of the edges in a single pulse of a reproduced binary signal can then, in certain circumstances, have a different spacing from one another than in the single pulse to be recorded. In addition, the phase response in the reproduced signal is not linearly dependent on the frequency. Thus, equalizers are used in the known reproduction systems for the purpose of improving the behavior of the reproduction electronics in the case of a step and/or phase response. Such equalizers deal with the incoming signals as analog signals. In principle, they are analog filters, which must be adapted to the parameters of the recording system (such as, e.g., tape speed, recording head characteristics, tape characteristics, etc).
In such known reproduction electronics, the equalizer is followed by a device for measuring the run length of the particular single pulse (step responses or 0 crossings), together with a circuit for quantifying the measured run lengths.
The primary disadvantage of this known reproduction electronics is essentially that the construction of such systems with equalizers is complicated. Furthermore, as stated, such systems must be set to specific parameters, and this setting procedure is labor-intensive. Further, if the parameters are modified, then resetting is necessary. In addition, several equalizers are often used in such systems and are connected in series and set to different values of one or more parameters of the system. However, such a solution is hardly feasible in reproduction equipment because it is prohibitively expensive and takes up an excessive amount of space in the equipment.